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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Posted on 9 March 2011 by dana1981

A "mass extinction" event is characterized as a period during which at least 75% of the Earth's species die out in a geologically short interval of time. In the past 540 million years, only five such mass extinction events have occurred, but according to a review by Barnosky et al. (2011) recently published in the journal Nature, there are signs that we may be entering a sixth such event.

These previous mass extinction events (also known as the "Big Five") are hypothesized to have been caused by key synergies such as unusual climate dynamics, atmospheric composition, and abnormally high-intensity ecological stressors (or in the case of the Cretaceous, an asteroid impact and subsequent effects).

Barnosky et al. note that scientists are increasingly recognizing modern extinctions of species due to various human influences, including some of the same effects which caused the Big Five:

Natural Extinctions

There are of course species extinctions which have nothing to do with human influences. Scientists have identified a "background rate" of species extinctions from the fossil record, which allows for a comparison to the current extinction rate, thus allowing us to assess the human impact on the rate of species loss. A widely-used metric is extinctions per million species-years (E/MSY), in which background rates are estimated from fossil extinctions that took place in million-year-or-more timeframes. The authors note that it is difficult to compare the current rate of extinctions, which are occurring over periods of just decades to centuries, to this background rate determined from periods millions of years.

That being said, the average E/MSY over the fossil record is approximately 1.8 (meaning on average, fewer than 2 species go extinct every million species-years), and the most common E/MSY over periods less than 1,000 years is zero. Bear in mind that these are species-years, and that there are an estimated 20 million species on Earth, so each year constitutes approximately 20 million species-years.

Current Extinction Rate

Branosky et al. find that over the past 1,000 years, the average extinction rate is 24 E/MSY (13x background). Breaking the data into 1-year bins, the maximum extinction rate over that period is approximatley 693 E/MSY (385x background). Clearly these values far exceed the background rate. And the worst case scenario, if all currently threatened species go extinct, results in a clear divergence from the natural extinction rate:

"In the scenario where currently ‘threatened’ species would ultimately go extinct even in as much as a thousand years, the resulting rates would far exceed any reasonable estimation of the upper boundary for variation related to interval length"

The authors also find that the extinctions over the past 500 years are happening at least as fast as the species extinctions which triggered the Big Five:

"Current extinction rates for mammals, amphibians, birds, and reptiles, if calculated over the last 500 years (a conservatively slow rate) are faster than (birds, mammals, amphibians, which have 100% of species assessed) or as fast as (reptiles, uncertain because only 19% of species are assessed) all rates that would have produced the Big Five extinctions over hundreds of thousands or millions of years"

Time to Worry?

The study also evaluated whether we are in (relatively) immediate danger of triggering an extinction event by evaluating a hypothetical scenario in which the Big Five extinctions occurred suddenly, over just 500 years rather than hundreds of thousands to millions of years. In this case, the extinction rates during the Big Five would have had to exceed 1,000 E/MSY; a value which we have not yet reached. However, Barnosky et al. note that if we consider a scenario where currently threatened species are inevitably extinct, the current extinction rate is almost as fast as the hypothetical 500-year Big Five extinction rates. In other words, if we lose all currently threatened species, we will be on a course for a new mass extinction event in just over 500 years.

In a similar hypothetical, examining how many more years it would take for current extinction rates to produce species losses equivalent to Big Five magnitudes, the authors arrive at a similar conclusion:

"if all ‘threatened’ species became extinct within a century, and that rate then continued unabated, terrestrial amphibian, bird and mammal extinction would reach Big Five magnitudes in ~240 to 540 years....This emphasizes that current extinction rates are higher than those that caused Big Five extinctions in geological time; they could be severe enough to carry extinction magnitudes to the Big Five benchmark in as little as three centuries."

Conclusions

The authors draw two main conclusions from these findings. The first is that although we're clearly in dangerous territory in terms of extinction rates, we still have enough time to reverse course, although doing so will be a very difficult task.

"First, the recent loss of species is dramatic and serious but does not yet qualify as a mass extinction in the palaeontological sense of the Big Five. In historic times we have actually lost only a few per cent of assessed species...It is encouraging that there is still much of the world’s biodiversity left to save, but daunting that doing so will require the reversal of many dire and escalating threats"

The authors' second conclusion is that if we continue on our present course, we could be headed towards a mass extinction event within a timeframe of just a few centuries. Therefore, it's very urgent that we steer away from our mass extinction course immediately.

"there are clear indications that losing species now in the ‘critically endangered’ category would propel the world to a state of mass extinction that has previously been seen only five times in about 540 million years. Additional losses of species in the ‘endangered’ and ‘vulnerable’ categories could accomplish the sixth mass extinction in just a few centuries. It may be of particular concern that this extinction trajectory would play out under conditions that resemble the ‘perfect storm’ that coincided with past mass extinctions: multiple, atypical high-intensity ecological stressors, including rapid, unusual climate change and highly elevated atmospheric CO2. The huge difference between where we are now, and where we could easily be within a few generations, reveals the urgency of relieving the pressures that are pushing today’s species towards extinction."

It's also important to bear in mind that takes a very long time to recover the biodiversity loss from a significant extinction event:

"recovery of biodiversity will not occur on any timeframe meaningful to people: evolution of new species typically takes at least hundreds of thousands of years, and recovery from mass extinction episodes probably occurs on timescales encompassing millions of years."

Summary

In short, human influences, including our impacts on climate change, are causing extinctions at a rate faster than the average during a mass extinction event. If we continue down our current path, we may face a sixth mass extinction event within the next few centuries. However, we're still relatively early along in the process, so although it will be a difficult task, there is still time to change course and prevent a huge loss in biodiversity. If we fail to do so, it may take millions of years to recover from the human-caused extinction event, and we're quickly running out of time to avoid this fate.

ClimateWatcher - you seem to be missing the point that these species are already going extinct. It's an observational reality. And climate change isn't the only anthropogenic factor behind the accelerated rate of extinctions, as the article notes.

ClimateWatcher seems to think there is only something to worry about if we lose most of the species. Losing 75-95% sounds pretty damn scary to me, and worse yet is preventable to some degree.

Also, one of those species may even be Homo Sapiens, but I understand that that possibility is of little concern to someone who will unlikely be around after 2050.....Anyhow I was being facetious, humans may not go extinct, but the hurting will start a very long time before event that is on the horizon.

#6@Albatross says:
" ... humans may not go extinct, but the hurting will start a very long time before event that is on the horizon. "

For communities who rely on particular species to support their traditional way of life, climate shift may not eradicate species, but may so modify the environment as to make those species unreachable by traditional means. For many Inuit communities, the hurting started a while back.

It's important to remember in all this that it doesn't take a large number of individuals to keep a species going. So, when we talk about an extinction event losing 80 or 90% of species, that is likely a much large percentage of the creatures on the planet.

That's what gets me about the idea of "adaptation." Yes, humans are quite adaptable and we might very well not be one of the species that goes extinct. But it might very well involve the overall human population rapidly dwindling to a small fraction of the number of people alive today.

Frankly, I'm not worried too much about humans going extinct. I'm concerned about the unprecedented misery inflicted upon people, who are yet born, in the transition to a dramatically reduced population.

ClimateWatcher - you seem to be missing the point that these species are already going extinct. It's an observational reality. And climate change isn't the only anthropogenic factor behind the accelerated rate of extinctions, as the article notes

Species are always going extinct at the background extinction rate.

Do consider that extinction is part of evolution. (traits that are liabilities are extinguished only by the extinction of those bearing the genes for those traits).

But there's not much evidence that the current extinction rate is anything other than the background rate.

You must find it truly bewildering that the Earth's glaciers and ice sheets are disappearing, if that's the extent of your watching. Remember we are concerned about climate - the weather averaged over longer time frames. It can cause changes in environmental conditions which are essentially permanent relative to the lifetimes of many species. Not just the lifetimes of bacteria.

Were species actually to be so sensitive, one would ask the obvious question, why didn't they all go extinct at the end of the last ice age? or at the Holocene optimum?

Why would you expect them to all go extinct?. Seems like a strawman argument to me. Regardless many species did go extinct during the ice ages . Seen any woolly mammoths walking around lately?.

The problem with the Anthropocene extinction is that we have fundamentally altered so many natural systems. Chopped down many of the world's forests and converted them into grassland., thereby removing a large chunk of natures natural sediment filter. On top of that, to feed humanity's rapacious appetite, much of the land has been converted to grow monoculture, or farmland to feed grazing animals used for food.

In order to achieve high productivity we have used fossil fuels to manufacture artificial fertilizers. These artificial fertilizers, which boost plant growth, contain high levels of nitrogen & phosphate which leaches readily into rivers and streams (remember we've crippled nature's natural filter). The excess nitrogen and phosphate boosts algal growth in waterways, because algae are essentially water-living plants. This causes eutrophication, i.e. we get algal blooms, which chew up oxygen in the water, when the algae die (they have short lifetimes) bacteria break down the algal remains and in the process further deplete oxygen in the water. It just so happens to be inconvenient to many species to not have any oxygen - if they can't escape they die.

This is also happening in coastal waters because ultimately the nitrogen and phosphate run-off ends up in the ocean. Guess what?, the coastal seas are becoming eutrophied as well, and there's the additional impact of those land use changes letting more sediment reach the coast, it blankets and chokes marine life in near-coastal waters in extreme cases (I've witnessed it for myself over the last 3 decades where I live). This is a world-wide problem. Harmful algal blooms are increasing, hypoxic and anoxic zones in the ocean are increasing (although not solely because of eutrophication)

And that's just one consideration. What about land use changes impeding species migration?. Toxic man-made chemicals in the environment?. Groundwater extraction?. Introduction of invasive species on a worldwide scale?, ocean acidification? (not a problem during the last few million years - no industrial civilization back then), the speed of warming? (much higher than the glacial/interglacial rate)

The speed of change and the numbers of changes we have made to natural systems should be of concern, but that's a value judgement I guess. These changes are well outside the conditions experienced on Earth for millions of years.

Your frenetic hand-waving changes none of this. When you start to understand how things operate in the natural world. It's hard not to worry. And personally I don't find this study wholly convincing, but hey, that's just one take.

Rob, I think your analysis is objectively correct (and GW is only a very minor component of the anthropic influence, if any). But .. so what ? we KNOW that the industrial civilization has profoundly impacted the environment. After all, it is enough to walk in a large city to see that natural systems have been fundamentally altered, there is no need for CO2 to explain that. But what is your conclusion ? that we should all abandon our cities and become again hunters and gatherers (finding a way to reduce the world population by a factor of 100 or so?) Human civilization is also part of the nature, like giant meteorites or hypervolcanoes. Should we really feel guilty about it ? nature doesn't know anything of what happens. Most planets to not harbour life AT ALL - and even life on the Earth is , by far, dominated by microorganisms and worms that don't care the hell what is happening with mankind. Mankind is exactly like other species - trying to survive and reproduce. It is much more successful than many other (although ants are not that bad) ... so what ?

Hard to believe that the probability of controlling these factors could possibly go up with the global population, and perhaps reducing the discussion on the whole to a simple formula that relates bio-stability to world population.

Since global warming is only one factor contributing to a possible mass extinction of species, (and as I have been told over and over that global warming is not a matter of over population), it would seem that by now someone (in this climate science community) has recognised this "minor detail" and come up with an acceptable figure (or recommendation)... peer reviewed and all. Or is that asking for too much?

"So what?": It's not a question of "guilt," it's a question of responsibility. We ARE the "management of the planet." Whatever happens, we're going to have to deal with it. We need to start taking seriously that responsibility now.

RSVP (16):

Before expecting other people to come up with a recommendation, it's appropriate to recognize the problem. That's going to take some public discussion, as there are still many people willing to claim that it's "no big deal," as evidenced on this very page.

An appropriate analogy comes to mind: If we were on a spacecraft journeying to another star-system and planet, and we saw these sorts of shifts and extinctions going on, would it be prudent to worry? You betcha.

Well, we ARE on a spacecraft (Spaceship Earth) journeying into the future. Things are beginning to go tilt, and the captain hasn't shown up to fix things. That's no mystery, because we've just gotten the memo: "Congratulations for deciphering this message! You're no longer just the passengers, you are the crew!"

This post does not even mention the extinction of large mammals caused by humans in the past. Most of hte lare mammals in Europe, the Americas and Australia were hunted to extinction by humans. Now the small animals are following in the path.

You don't seem to be all that bothered by the prospect of species extinction & natural selection. Thing is, homo sapiens is nothing special, such evolutionary pressures apply to us, too (although we are capable of modifying our environment somewhat to suit us).

The thing is, as I saw it put recently: Evolution works by death.
"Survival of the fittest" means the non-fit don't survive to breeding age - in the case of humans, that's about 12-16 years of age.

What makes you so sure that your grandchildren & great-grandchildren will be in the "fit" category and not the "non-fit" one?

The thought that we might see that kind of evolutionary pressure on the human race again saddens me, even more so that many "skeptics" don't seem to care about the hundreds of millions of people whose lives are at risk if even half of the IPCC projections come to pass. We've just spent the past couple of centuries battling to decrease mortality rates, especially in children. It seems more than a shame to throw that progress under the "business as usual" bus.

Don't mock mass extinctions, without the last one we wouldn't be here!

I am not clear why people regard mass extinction as a bad thing. While mass extinction would make the world less interesting, with fewer of the charismatic megafauna to see on TV and in the zoos, the species that are useful to us should survive as long as we do, with our protection. So would another mass extinction do us much harm compared to all the other damage we are doing to ourselves? We don't particularly need millions of species, and neither does the Earth.

Really? first, who told that ? and second, who tells what the planet wants ? as far as I can see, our vision of the planet is mainly our own anthropomorphic projection. We care about mammals, some birds, some other vertebrates, not so much about microorganisms for instance. But ok, let's assume we have to take care of all these species. Does it mean that we should abandon our cities and let bears and wolves come back? or not? why not ?

Bern : i just notice that GW is a minor component of species extinction, and that the main reason is just demography - and the need to feed billions of people, plus all the minerals we extract from the earth to make all the gagdets of civilization. For instance, electric cars need as many roads and as oil powered ones, and a lot of metals or plastics and so on. And if you want to spare lives of hundreds of millions of people (barring the fact that reducing the use of FF may be much more destructive for them than GW), this will eventually WORSEN the demographic pressure on natural resources.

So how far do you think we have to go to let "nature" go back to its original state?

The whole picture for me is that many people adopt (over)simplified thoughts, reducing all the problems to a simple numbers ("average temperature", "CO2 concentration", "number of living species") and basically saying that the only thing to do is minimizing (or maximizing) these numbers, whatever the consequences are. Reality is much more complex - which explains that these people persistently complain about the fact that nobody seems to obey their simple thoughts.

Giles@21 Yes really, we manage the planet primarily in our own interest. Who told us that? Nobody, we as a species have decided that we are in charge. Who tells us what the planet wants? Nobody, and we probably wouldn't listen anyway. However, we are managing the planet in our interest and it happens to be in our long term interest to preserve the natural environment in a state that best supports us. That happens to include avoiding mass extinctions. No "anthropomorphic projection" is required, just thoughtful self-interest (as a species rather than as individuals) will do nicely.

"So how far do you think we have to go to let "nature" go back to its original state?"

As far as it is prudent for our long term interests as a species.

As to "simple thoughts" the underlying "simple though" is that we should avoid unnecessary change in our environment, as change requires adaption, which may not be pleasant. The numbers help focus on what we need to do to avoid unnecessary change, but that is about all.

pikaia, more species means more resilience, more 'redundancy' or 'slack' in the system. a system of many species eating many others in a varied cycling web is going to be much less likely to collapse than one of just a few components. that's why i'm keeping a close eye on krill.

DM : I can totally agree with what you're saying - the only thing we'll do is managing the planet in our own interest. Do you agree at turn that it cannot easily converted into a "simple" minimization/maximization of a single index like those I mentioned above ?

dana, it's possible all the extinctions are down to co2, even the impact(s);
the deccan traps were opposite the k/t impact site, and there seems to be a depression in eastern antarctica that might be a truly huge crater directly opposite to where the siberian traps were at the time of the permian extinction.

Giles@24 The key issue is weighting our short term interests against our long term interests (sadly human nature generally tends to focus on our short term interests as individuals at the expense of our long term interests as a society/species, which is why we are faced with the problem under discussion).

Whether you can convert that into a simple maximisation/minimisation problem depends on the level of abstraction/complexity at you need to work. Focusing on CO2 emissions, for the vast majority of us, is entirely sensible. While CO2 is not the only problem, it is the one we can control most easily as individuals; the problem of climate change can be considerably alleviated by focussing on that one issue first. It is a matter of prioritization; it is much better to take action that solves most of the problem, than doing nothing to address the problem because we spend all our time worrying about the complexity of the fine details. So, no, I don't agree - single indices are useful and have their place.

What makes you so sure that your grandchildren & great-grandchildren will be in the "fit" category and not the "non-fit" one?

Nothing. That's what being a life form entails.

The thought that we might see that kind of evolutionary pressure on the human race again saddens me,

Evolutionary pressure is what lead to human brain size and opposable thumbs! Be glad for evolution!

You are probably too young to remember the rock group Devo,
which was short for DE-volution - a lament that evolutionary pressures were lacking not too high.

even more so that many "skeptics" don't seem to care about the hundreds of millions of people whose lives are at risk if even half of the IPCC projections come to pass.

The observed trends in temperature increase are all below even the rate of the 'Low Scenario' from the IPCC. And even if temperature reached the 'Low Scenario' that's still less than the temperatures of the Holocene Climatic Optimum. It was during the HCO that human civilization advanced! Remember the Mesopotamian 'Cradle of Civilization?'.

00

Moderator Response: [DB] You are incorrect on many counts.

Firstly, current temperatures have already equaled those of the HCO, AKA the Holocene Altithermal (Hansen, 2011). Secondly, emissions are trending at the IPCC "High" emissions level. Lastly, it was exactly the climate stability of the HCO that allowed the development of agriculture. With the warming of the planet still in the pipeline, and the ensuing desertification to come as a result, all that remains is to update the following graphic with an arrow and the label "Agriculture Ends Here":

ClimateWatcher @ 10... Do you honestly not understand the difference between weather and climate? It's really hard to take you seriously on anything when you don't even understand such elemental aspects of climate.

Gilles,
"many people adopt (over)simplified thoughts, reducing all the problems to a simple numbers"

I suspect that if we did not discuss such numbers, you would object that since we don't know an 'average temperature' or 'co2 concentration,' we can do nothing about them.

Your arguments are tending more and more to the non-scientific: 'I live in the real world,' 'who tells what the planet wants?' etc. Then you turn around and suggest "reducing the use of FF may be much more destructive for them than GW," which is either blatant speculation or the result of some detailed knowledge of the human condition now and in the future. If you have that knowledge, please share; absent that, I assume speculation is the case.

Some would argue that we are an intelligent species; certainly we know how to count and therefore how to measure. Without measurement and 'indices,' we cannot make educated decisions. In the context of this post, without a count of living species, we cannot determine the ecological consequences of our actions.

Because in the real world, actions have consequences; some are beneficial, others tragic. If the part of the real world in which you live does not work that way, I envy your position.

ClimateWatcher @ 27... Your arguments here are essentially the same as to say, "Well, humanitarian atrocities are a normal process that humans go through once in a while, so what-the-heck."

Regarding keeping temperatures below the HCO, that's not the concern here. We are currently about 1C below the HCO. If we could hold global temperatures steady at 2C over preindustrial, that's is essentially right about the danger point. The concern here is the business-as-usual scenario that puts us at 2 doublings of CO2 over preindustrial. Add in slow feedbacks and permafrost melt and that, my friend, has the ring of "game over" written on it.

If you're of the DEVO generation (as I am) then you and I are going to have no problem. This is unlikely to affect us in a dramatic or catastrophic way. But my kids, who are currently 5 and 7, when they are my age this issue is going to be the only thing they are dealing with. Unless we do something about it now.

DM : the fact that even you -and all climatoalarmists - do not reduce the problem to a simple minimization of CO2 production is proven by the simple observation that the minimum is very easy to compute : it's zero. But , as everybody knows , "nobody claims we should stop totally using FF just now", and "nobody claims we should go back to Dark Ages". Okaaay. If nobody claims that, it means that everybody is in favor of some kind of compromise between burning fossil fuels, but not too much. So it is NOT a simple minimization.it's a matter of compromise. Just as nobody urges to leave our cities and go back into the woods. Or stop using cars. Or kill all babies to stop demographic expansion. It's ALWAYS a matter of compromise.

Now the real question is : if it is all matter of compromise, do you have a definite answer of WHERE the compromise lies exactly ? Mr J.H. says 350 ppm ? Mr XYZ says 450 ppm are ok? some think that 550 ppm or even 700 ppm maybe not that bad after all? Mr KA says that there is no risk anyway that we could reach more than 500 ? do you have a SCIENTIFIC answer ? I'm afraid not. Because who can the hell say how mankind will live in 50 or 100 years? just now, you have mainly billions of people either starving for death or just being hungry, subject to all kinds of diseases because they just don't have drinkable water, and so on. WTF do they care about who will live in 100 years nears seas they will never know ? they don't know where their children will live , or even if they will live.

Mucounter : "Then you turn around and suggest "reducing the use of FF may be much more destructive for them than GW," which is either blatant speculation or the result of some detailed knowledge of the human condition now and in the future. If you have that knowledge, please share; absent that, I assume speculation is the case."

"Growth of about 9 percent per annum since the late 1970s has helped to lift several hundred million people out of absolute poverty, with the result that China alone accounted for over 75 percent of poverty reduction in the developing world over the last 20 years. Between 1990 and 2000 the number of people living on a dollar per day fell by 170 million, while total population rose by over 125 million.

China's market-oriented reforms over the last two decades also dramatically improved the dynamism of both the rural and urban economies and resulted in substantial improvements in human development indicators.

Official estimates of the adult illiteracy rate fell by more than half, from 37 percent in 1978 to less than 5 percent in 2002, and, indicative of health indices, the infant mortality rate fell from 41 per 1,000 live births in 1978 to 30 in 2002. China has entered the World Trade Organization, shifted its policy orientation from pure growth to overall well being (a xiaokang society), and made the historic switch from net taxation of agriculture to net subsidization."

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Response: This conversation has gotten far enough off topic to be moved to the thread "It’s too hard." Everybody, not just Gilles, please do so.

Does it mean that we should abandon our cities and let bears and wolves come back?

I've asked before, and I'll ask again: what is it with "skeptics" and strawmen? I can't be the only one who's sick of this inactivist boilerplate about how addressing a given environmental problem — i.e., acting like the responsible, intelligent people we claim to be — is going to force us all to gnaw roots while shivering in caves.

If you ask me, people who find it emotionally easier to forfeit biodiversity and ecosystem services than to question economic dogmas founded on a basic denial of science and logic will probably do a lot more for the cause of city abandonment than anyone who's counseling climate action now.

Several of the comments in this thread remind me of a passage from Dominion by Matthew Scully, who was one of George W. Bush's speechwriters:

It is the same fundamentally vulgar vision of man that conservatives elsewhere so earnestly worry about....man the all-conquering consumer facing the universe with limitless entitlements and appetites to be met no matter what the costs....

My National Review colleague Jeffrey Hart, a professor at Dartmouth College, captured the attitude nicely...."It is depressing," he writes, "to hear cigar-smoking young conservatives wearing red suspenders take a reductive view of, well, everything. They seem to contemplate with equanimity a world without lions, tigers, elephants, whales. I am appalled at the philistinism that seems to smile at a future consisting of a global Hong Kong."

Another thread, and yet more examples of 'skeptics' and contrarians talking through their hats, obfuscating, arguing strawmen and derailing the thread. The substance of their argument, if any, seems to boil down to it has happened before, it is not bad.....even the ostriches must be feeling threatened by this behaviour.

How about actually making an effort to critique the methodology etc. (anything scientific) about Barnosky et al. (2011). And by critiquing i do not mean hand waiving, I mean substantive, scientific critique with supporting evidence and citations.

Then, at that point you may perhaps consider submitting a comment to Nature demonstrating how they (allegedly) got it all horribly wrong.

In an area (e.g. your back yard) where the existing climate has such fluctuations, the ecosystem adapts to them.

The problem areas are twofold. Firstly it is the movement of climatic zones through the latitudes, including precipitation, not just temperature. Secondly, it is the rate of such transitions that is absolutely critical i.e. if the rate of change outpaces adaptation, then decimation of ecosystems occurs.

You should be concerned. Those self-same ecosystems make agriculture possible!

Have you read "Extinction" by Dr. Michael Boulter? If not, I recommend it.

"It seems that the largest genomes, the most complex physiology and neurology don't guarantee a permanent place on the throne of biodiversity. What we naively saw as an evolving hierarchy does not have ourselves, the human race, in its upper branches."

This statement missing the mark on so many counts. So the old, warming equals diversity argument? If so, deserts should be teaming with life, more so than other more temperate eco zones.

Also, we are warmer than the HCO and will continue to warm well beyond that. It is not so much what is happening now, but what is very likely to happen down the road that is an issue. also, during the HCO there were not 7 billion plus bi-pedaled primates walking around to feed.

it means that everybody is in favor of some kind of compromise between burning fossil fuels, but not too much.

I'm not so sure about that. Certain people — small in number, but with a significant public influence - seem to reject any environmentally based limitation on burning fossil fuels.

some think that 550 ppm or even 700 ppm maybe not that bad after all?

There's virtually no belief so dangerous, silly or unsupported by evidence that you can't find "some" who accept it. However, we're really not interested in the full range of idle speculation here. We're interested in what's plausible. If you can present plausible scientific support for the view that 700 ppm is "not that bad," please do so. Otherwise, you're blowing smoke.

Because who can the hell say how mankind will live in 50 or 100 years?

Another strawman. If AGW will cause droughts in a given region, we can say that people in those regions will tend to live in conditions of drought, with the suffering and food insecurity that entails. If a species vanishes, we can say that people will have to do without the benefits of that species (and this would of course include species whose benefits are currently unknown). If intense heat waves will occur more regularly, we can say that this is a serious problem people will have to deal with. Appealing to ignorance in this way strikes me as a typical attempt to cling to the pleasures of irresponsibility.

Well there's that, but also when environmental conditions change enough to induce a die-off, extinction isn't an instantaneous event. Oblivion for species can take a handful of generations to manifest itself. See discussion of extinction debt in the scientific literature.

Even if species manage to survive, for extreme changes very few individuals will possess the necessary traits/genes for survival, so what we would expect to see is populations crash, and a very long recovery period.

How any of this is of any use to a global society trying to feed (or not) 7 billion people, the AGW skeptics have yet to explain.

RSVP,
I don't know about everyone, but what I see is that humans are facing a triple threat of overpopulation, climate change, and peak oil.

For instance, if there were only a couple million of us on the planet, we could consume several times as much fossil fuel energy as the average American and it would have little impact on the planet's climate. And, we could eat whatever we wanted and it would make little difference as well.

My guess is that food production is pretty well optimized according to the average temperature and rain patterns that have existed for several thousand years. So, I'm guessing that if they change, and especially if there is no stabilization, and the change continues, there will be a drop in production. The earth's carrying capacity for the human population will be lowered.

Looking at the trend lines, our need for food, as the population grows, is gaining on our capacity to produce food.

A lot of our food production is heavily dependent on petroleum products including not just the gas to drive the tractors, but also fertilizers and pesticides.

The three factors will combine to cause rises in food costs and shortages.

As the price of food increases, at some point there will be an awful lot of angry, hungry people in the world, and they will blame their misery on someone else. At first it will be their own leaders, but will expand to include the ones who aren't hungry, most likely the Americans, Australians, and Russians since they most often have food surpluses. (Although there is an obvious counter-example to that this year.) Anyway, what was the quote I read, historically, when humans are faced with starvation or raiding, they raid every time. If some of the raiders have large armies or nukes, there could be a bit of an over-correction of the population versus carrying capacity ratio.

It all comes down to how well a species can take energy from its environment. I should probably explain that I don't just mean energy that we use on the electric grid. To a predator, the prey is energy; to an herbivore, plants are energy; to plants, sunlight is energy. All species compete for energy. If a species is more adept at gathering energy than its competition, it has more offspring than its competition. Humans are the most successful invasive species I know of because they are so adept at consuming whatever is available.

It would seem that our need to reproduce combined with our skill at utilizing whatever resources are available would lead to extinctions of many other species regardless of our impact on the climate, simply because we take to ourselves the energy resources that other species need. I am not saying we should be complacent about it, but I don't see how we can go from a few million to over 6 billion and counting without knocking off a few other species.

I see climate change as a contributing factor to species extinctions as well as overpopulation, but I can make no claim is to which is more significant.

I suppose what we are haggling over is the quantity of human life versus the quality of the lives that are.

A catastrophe for pseudo-skeptics would be higher taxes, more expensive fuel, or horrors, regulations. Raising the global mortality rate by several million a year is just fine so long as they are long way away and preferably Muslim.

What keeps being forgotten in discussions about extinctions etc is that species extinctions are not discrete events.

All species rely on other species for their survival - be it food, pollination, shelter, symbiotic relationships, etc. The 'food chain' or ecosystem is like the child's game of 'pick up sticks'. Sometimes, you can remove a single stick from the pile and not much happens. Other times, the removal of one stick causes others to move and fall. Eventually, if you remove enough sticks, the whole pile comes crashing down.

The ecosystem is the same. Sometimes the extinction of one species can essentially go unnoticed. However, in other cases the extinction of a species will cause cascading trophic events and can cause multiple other species to go extinct or to undergo substantial change. Eventually, if enough critical species go extinct, the whole system falls apart and there is nothing anyone can do to prop it up.

What's worse, we only have a very limited understanding of which species are the critical ones. We do know there are some species such as phytoplankton which underpin almost all life on Earth - and we do know they are undergoing dramatic changes right now as a result of climate change and other anthropogenic influences. But what exactly that will mean for life as we know it is unclear. There are others - bees and coral for example. But we just don't know how many other species are out there that could cause the pile to collapse, nor what their current circumstances or vulnerability to change are.

We are tampering with forces we don't understand, and which can have profound effects on our way of life. This is not about a few feet of sea level rise, or higher insurance premiums because of more extreme weather events. Despite our grandious posturings, we are an animal species just like every other animal species, and subject to the same ecosystem influences. Human survival of the current round of extinctions is not guaranteed.

I don't know why this story appears here, extinctions of the overwhelming majority of species in the last 400 years is nothing to do with climate change, it is simply about the ignorance of man not appreciating the impact our activities have. I do not deny man is responsible for a large number of extinctions, but I do think it is stretching to;

1) link extinctions to global climate change (man made or natural) at this time.

As far as we know, there have been 5 events causing mass extinction of biota. Those events all have at least 5 things in common.
1. Their effect was global
2. All caused atmospheric changes
3. In geological terms they occurred rapidly
4. All resulted in loss of >50% of plant and animal species
5. All were characterised by destruction of habitat.

The most serious of these events was the Permian Extinction which resulted in the loss of >90% of plant and animal species. So severe was this event that rebound of life-forms took 15 million years.

In this and other extinction events, deep ocean warming, possibly caused by warming of the earths mantle, resulted in the melting of clathrates. This resulted in triggering of the so called “Methane Gun”, the release of massive amounts of methane from the ocean bed over a prolonged period, though possibly only a few centuries.

As this methane percolated from the ocean bed to the surface, it oxidized to form CO2 and in the process deoxygenated ocean waters, causing the death of marine flora and fauna on a massive scale. Both gases may have become atmospheric pollutants, though possibly not as serious as the release of aerosols from volcanism or asteroid collision.

Atmospheric pollution would have prevented or at the very least limited photosynthesis and produced rapid cooling, at some stage countered by diminution of aerosols and increase of CO2 and other greenhouse gases.

The most vulnerable to extinction events are plants and animals unable to rapidly adapt to increasing atmospheric pollution, those with small populations or large body size and those dependent on limited diet.

It is not clear that we are now at the start of an Extinction Event but we may well be, though on this occasion one triggered by the human species rather than “natural” volcanism.

What is clear is that if unchecked in the very short term, greenhouse gas pollution will cause relatively rapid global warming having the same effects as those characterising earlier extinction events.

Shakhova (2010) has already reported that warming of the ocean and seabed off the Siberian coast is already beginning to melt methane clathates. The result is that atmospheric concentration of methane in the Arctic has already reached the highest levels known in 400,000 years.

No less concerning is her estimate that destabilisation of offshore permafrost could result in accelerated melting of clathates with an estimated capacity to release 70 billion tones of methane into the ocean. In addition, melting of Siberian marshland permafrost has potential to increase this total.

Significant quantities of methane from shallow offshore waters are likely to reach the atmosphere without oxidizing. The bulk, from deeper water, would oxidize before reaching the surface, reducing oxygen in the Arctic Ocean. Both would add to the level of CO2 in the atmosphere further accelerating global warming, placing the environment of biota under increasing stress.

It is possible that we may not be approaching the next Extinction event but the signs are ominous and the past provides a stark warning of what lies ahead unless we act promptly to curb greenhouse gas emissions.

LandyJim #46 - you're free to think whatever you like. I merely reported on a study in which the scientific experts disagree with your beliefs on the subject. Agnostic #47 - good summary. As you say, there are clear signs (the rapidly accelerating extinction rate) that we're on a very dangerous path.

"The authors' second conclusion is that if we continue on our present course, we could be headed towards a mass extinction event within a timeframe of just a few centuries. Therefore, it's very urgent that we steer away from our mass extinction course immediately."
(My italics)

LandyJim #46 complains saying that

"extinctions of the overwhelming majority of species in the last 400 years is nothing to do with climate change" (my italics)

I find that it's always worth reading the article before commenting on it.

I am posting in support of Agnostic@47. I recommend rereading that post rather than this. This is just a footnote.

We are all aware that the surface Arctic Sea Ice is disappearing.

As the surface sea ice disappears, the heat accumulating in the ocean has to do something.

It is quite likely to begin to melt the seabed. This is composed of sea water that has frozen in the presence of an abundance of methane. When it freezes, it the water traps the methane in a chemical lattice. This substance is called a methane clathrate.

When surface sea ice melts, 1 litre of frozen water (ice) becomes one litre of liquid water. This matters in various ways that are discussed all over the net...

For "litre" substitute "cubic kilometre" in the sentence above, and you are then staring at the scale of this problem.

I should note that, b-----r the greenhouse effect of methane. It is a poisonous gas, and explosive.

Furthermore, if the East Siberian shelf does begin to melt, it is very possible that there are very very large, very shallow deposits of gaseous methane which have been capped for some millenia by the solid methane clathrates above them.

Should any one of these gas fields collapse, and vent into the atmosphere then:

1. there would be some danger of the atmosphere becoming anoxic for the purposes of mammalian respiration;

2. there would be a near certainty of an Arctic ocean tsunami, which would be highly likely to cause much more extensive damage to the sea bed...

For any Republicans on here who are now delighted to learn that their vehicles will shortly be working better due to a greater level of methane in the atmosphere, I should perhaps point out that the infernal combustion engine also requires an abundant intake of oxygen to work at maximum efficiency...

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Moderator Response: [Daniel Bailey] Welcome to Skeptical Science. Your contributions to the dialogue at Neven's are appreciated and will be a welcome addition here. I must add some qualifiers and cautions to your observations: while what you point out would seem to be an obvious possibility, the probability is highly uncertain. Further research and monitoring is needed. But the fact that what you point out cannot be dismissed out of hand is a both sobering and cautionary tale to all.